/Engine/Source/Runtime/SlateCore/Public/Widgets/SWidget.h
Gets whether or not any users have this widget focused, and if so the type of focus (first one found).
The optional will be set with the focus cause, if unset this widget doesn't have focus.
[TOptional](API\Runtime\Core\IO\TOptional)< EFocusCause > HasAnyUserFocus() const